That's assuming a chopper with a piston engine, right? I'm pretty sure most helicopters today have turboshaft engines, they'll run as long as there's fuel and air.
I mean... yeah? There is definitely a switch that initiates rotation through ground power or APU and then fuel is introduced at the appropriate limit. Fuel can be removed and/or the electrical power that ignites the fuel can be switched off as well.
So there's actually multiple switches capable of turning off the engines.